Challenges threatening the upcoming 2020 census could put more than 4 million people at risk of being undercounted in next year's national head count, according to new projections by the Urban Institute.

The history of the U.S. census asking about people's citizenship status is complicated.

Many of the stops and starts have been unearthed as part of the legal battle over the decision by Commerce Secretary Wilbur Ross, who oversees the Census Bureau, to add a citizenship question to the 2020 census.

If the Trump administration gets its way, federal law will require this question to be asked of each person living in all of the country's households in 2020: "Is this person a citizen of the United States?" It's been close to 70 years since a citizenship question has been included among the census questions for every U.S. household.

In fact, the U.S. census has never before directly asked for the citizenship status of every person living in every household.

Three federal judges have ruled that the process the Trump administration followed in pushing to add a citizenship question to the 2020 census failed to meet the mark.

In Maryland, U.S. District Judge George Hazel summed it up as "woefully deficient," while U.S. District Judge Richard Seeborg in California called the administration's efforts to find a justification for the question "a cynical search."

The justices of the U.S. Supreme Court appear split along ideological lines on whether a citizenship question can be included on forms for the upcoming 2020 census.

Based on their questions during Tuesday's oral arguments at the high court, the justices appear ready to vote 5-4 to allow the Trump administration to add the hotly contested questions to forms for next year's national head count.

For the final months of 2020 census preparations to continue as planned, the Census Bureau says it is counting on the U.S. Supreme Court to resolve the legal battle over the citizenship question by June. But a new appeal filed by plaintiffs in one of the Maryland lawsuits over the question could complicate that timeline.

Speakers of Arabic — one of the fastest-growing languages in the U.S. — will have one fewer barrier to participating in the upcoming 2020 census.

For the first time, the federal government is planning to officially collect census responses in Arabic along with six other new language options for the head count, including French, Haitian Creole, Japanese, Polish, Portuguese and Tagalog.

New security measures at the Department of Defense that limit the release of military records about U.S. troops deployed abroad could put the accuracy of the 2020 census "at risk," according to a newly released internal Census Bureau document.

The Supreme Court has agreed to decide whether the Trump administration can add a citizenship question to the 2020 census. The decision grants the administration's request for an immediate review of a lower court's ruling that stopped plans for the question. A hearing is expected to be held in April.

The Trump administration is planning to ask the Supreme Court to review a lower court's ruling that blocks the addition of a citizenship question to the 2020 census, according to a Justice Department filing released Tuesday.

Ross, who oversees the Census Bureau, is set to appear at a March 14 hearing on Capitol Hill before the House Committee on Oversight and Reform, the committee's chairman, Rep. Elijah Cummings, D-Md., announced Tuesday.

A federal judge in New York has ruled against the Trump administration's decision to add a citizenship question to the 2020 census.

U.S. District Judge Jesse Furman ordered the administration to stop its plans to include the controversial question on forms for the upcoming national head count "without curing the legal defects" the judge identified in his 277-page opinion released on Tuesday.

Allegations of cronyism, wasteful spending and other misconduct are roiling a little-known federal agency in charge of producing and distributing the government's official documents, including paper questionnaires for the upcoming 2020 census.